With the increase in world energy demand, rational development and utilization of crude oil has caused more and more attention, the demand on crude oil output and recovery efficiency is also getting higher and higher. The conventional (primary or secondary) crude oil recovery process generally recovered only ⅓ of the geological crude oil reserves, with about ⅔ thereof failing to be extracted. Therefore, with the increasing tense in energy consumption, enhanced oil recovery has become an important topic in the research of crude oil recovery.
The tertiary oil recovery technology is an effective process for enhanced oil recovery. Specifically, among tertiary oil recovery technologies, the chemical enhanced oil recovery (CEOR) technology represents a very important and large-scale implemented technology, including the polymer flooding technology, the surfactant flooding technology, the alkali water flooding technology and a combination thereof. The CEOR technology makes use of the combination of physical and chemical effects, wherein the chemical action mainly resides in reducing the interfacial tension between a flooding fluid and crude oil. A surfactant contains both lipophilic (hydrophobic) and hydrophilic (lipophobic) segments, when dissolved into water, mainly adsorbed at the oil-water interface, whereby significantly reducing the oil-water interfacial tension (IFT). The reduction in the oil-water interfacial tension indicates that the surfactant is capable of reduction the cohesive force inside crude oil, dividing larger oil droplets into smaller ones, whereby increasing the passing rate of crude oil through a pore throat. The flooding function observed with a surfactant is further indicated by the effects like alteration in the surface wettability of oleophylic rock, emulsification of crude oil, increment of the surface charge density and oil droplet coalescence, all of which explain why the surfactant has been identified as a critical component in a flooding fluid.
However, the prior art flooding fluid for tertiary oil recovery suffers from such problems as poor interfacial activity of the surfactant component, leading to a relatively lower oil displacement efficiency for the flooding fluid produced therefrom, an over-complicated composition with the flooding fluid, which makes difficult the demulsification of the recovered liquid and the treatment of produced water; necessarily containing an inorganic alkali, which is harmful to the reservoir and oil wells, leading to corrosion of equipments and pipings. Further, an inorganic alkali will significantly decrease the viscosity of a polymer component, then a relatively higher amount of polymer has to be used to achieve a predetermined level of viscosity, which increases the overall cost of oil recovery. The prior art surfactant component is insufficient in the tolerance to elevated temperatures, and the tolerance to high salinity and high total dissolved salt (TDS), and tends to generate precipitation during compounding due to its poor stability.
Therefore, there is still a need for a surfactant composition, which is deprived of the problems in association with the prior art, and shows improved interfacial activity and stability as compared with the prior art.